Fluorination of hydrocarbons



Patented Dec. 18, 1951 FLUOBINA'I'ION F IYDIOOAIBONS Gerald M.Wlii

tlnamwillllngtemnel allgnor toE.I.duPontdcNemeure&0ompany,Wilmington,DeL, a corporation of Delaware N 0 Drawing. Application November 2,1949. 8011;] N0. 125.171

8 Claims. (Cl. 2H5

This invention relates to a new process for the preparation offluorinated hydrocarbons.

This application is a continuation-in-part of my application Serial No.108,041, iiled August 1, 1949, now abandoned.

The conventional method for preparing fluorinated hydrocarbons consistsin reacting a chlorinated or brominated hydrocarbon with a fluorinatingagent. such as antimony trifluoride or hydrogen fluoride, whereby thehalogen present in the hydrocarbon is replaced by fluorine. This has thedisadvantage of being an indirect process. Elementary fluorine has beenused to a limited extent for the direct fluorination of hydrocarbons buthas the disadvantage that the reaction is difllcult to control.

This invention has as an object a new method for obtaining fluorinatedhydrocarbons. A further object is a process for preparing fluorinatedhydrocarbons by direct reaction of a hydrocarbon with a fluorinatingagent. A further object is a new method for preparing vinyl fluoride andethyl fluoride, and particularly the former, by oxidative fluorinationof ethane. Other objects will appear hereinafter.

In accordance with the present invention the above objects areaccomplished by heating a mixture of a parafiin hydrocarbon. hydrogenfluoride. and oxygen to reaction temperature. within the range 325-700C., in the presence of a salt or oxide of a variable valent metal as acatalyst.

A convenient method for carrying out the process consists in passing agaseous mixture of the hydrocarbon, hydrogen fluoride and oxygen througha heated Inconel tube containing a bed of the catalyst. For best resultsa small amount of hydrogen bromide or other "promoter" is added to thegaseous charge. After passing through the reaction tube, the reactionmixture is separated into its components. for example. by condensing theoil-gas and then subjecting it to fractional distillation. In general amixture of fluoro-substituted hydrocarbons is obtained.

The process is illustrated more fully in the following examples.

Example I A mixture of methane, 40% hydrogen fluoride, 30% oxygen, and10% hydrogen bromide (all on a volume basis) was passed at a rate oi 10liters/hour through an Inconel tube, which was of 30 in. length and of 1in. internal diameter and which contained 140 cc. of copper oxide onalpha-alumina as catalyst, heated to 488" C. The contact time of thegaseous mixture with the heated catalyst under these conditions wasapproximately 18 seconds. The oil-gas, i. e.. the gaseous mixture comingfrom the reaction tube. was condensed in a series of cold trapsmaintained at -195 C. After five hours operation.

2 10 cc. of condensate was collected in the traps. This condensate wasdistilled in a low-temperature Podbielniak still with the followingresults:

Mole Per Coat of Total Gas Distilled Boiling Point Composition Thefluorine-containing hydrocarbons were identified by boiling point andinfrared absorption.

The catalyst used in this example was prepared by soaking 500 parts byweight of alphaalumina in a solution of 150 parts by weight of cupricnitrate dissolved in parts by weight of water. This mixture was heatedfor 2 hours at 500 C. in a stream of oxygen prior to use.

Example I] Composition Emmple III This example was carried out undersubstantially the same conditions as Example I except that the reactiontube was heated to 550 C. and the catalyst was obtained by soaking 300parts by weight oi alpha-alumina in a solution of parts by weight ofchromic nitrate in 60 parts by weight of water and heating theimpregnated sluminaatSOO'Qi'oronehourinastreamof 3 ongen prior to use.The product oil-gas contained 4% trifluoromethane and 0.8%difluoromethane according to infrared analysis.

Example IV A mixture of 33.3% methane, 44.5% hydrogen fluoride, and22.2% oxygen (on volume basis) was passed at a rate of 9 liters per hourthrough an Inconel tube identical with that described in Example I butcontaining 140 cc. catalyst prepared by soaking 400 parts by weight ofalphaalumina in a solution of 90 parts by weight of cupric nitrate and10 parts by weight of lead nitrate in 80 parts by weight of water. Thetemperature of the tube was 542 C. and contact time approximately 18seconds. Analysis of the oil-gas by infrared showed about 1% each oftrifluoromethane and difluoromethane, with trace of monofluoromethane.

Example V A mixture of 28% ethane, 29% hydrogen fluoride, 41% oxygen,and 2% hydrogen bromide (percentages in terms of volume) was passed at arate of 44 liters/hour through an Inconel tube. which was 30 in. longand 2 in. in internal diameter and which contained 650 cc. 0! copperoxide on alpha-alumina, heated to 550 C. The contact time of the gaseousmixture with the heated catalyst was about seconds. The oilgas waspassed through dry sodium fluoride to absorb unreacted hydrogenfluoride, then through soda lime to absorb carbon dioxide, next throughDrierite (calcium sulfate) to remove water, and flnally into two traps,the flrst cooled to 78 C. and the second to -l95 C. After 2 hoursoperation, about 1 cc. of liquid (apparently vinyl bromide) collected inthe 78 C. trap and about cc. of solid in the 195 C. trap. The solidprodnot, on distillation in a Podbielniak still, was found to consist of63% of a mixture of methane and carbon monoxide; 16% of a fractionboiling at l10 C. and consisting largely of ethylene but containingsmall amounts of methane and trifluoromethane; and 18% of a mixtureboiling at 90 to 42 C., mostly at 98 to -94 0., consisting of ethane,trifluoromethane, and traces of difluoromethane and monofluoromethane(identifled by infrared analysis).

Example VI A mixture of 21.8% methane, 43.5% hydrogen fluoride, 32.7%oxygen, and 2% hydrogen bromide (by volume) was passed at a rate of 20liters per hour through an Inconel tube oi. 1.5 inch diameter and inchlength containing 340 cc. of the copper nitrate on the alumina catalystdescribed in Example I. The product oil-gas contained 10%trifluorornethanc and 6.5% difluoromethane with an indeterminate amountof monofluoromethane based on infrared analysis. This corresponds to a23.8% yield of fluoromethanes based on the methane consumed, or a 25.5%yield based on the hydrogen fluoride.

Example VII A catalyst was prepared by soaking 350 cc. (617 g.) ofalpha-alumina in a solution of 300 g. Fe(NO:):-9H:O in 130 cc. of water.This mixture was placed in an Inconel tube, 30 inches in length and 1%inches internal diameter, and heated in oxygen at 500 C. for two hoursand then inhydrogen fluoride for /2 hour. A mixture oi 20% ethane,hydrogen fluoride, 30% 0 188. and 10% hydrogen bromide (all on a volumebasis) was then passed over the catalyst at a rate of 21 liters/hour andat a temperature Example VI" A catalyst was prepared by soaking 350 cc.(617 g.) of alpha-alumina in a solution of 200 8. of lead nitrate in 250cc. of water. A mixture of 30% ethane, 40% hydrogen fluoride, 20% oxygenand 10% hydrogen bromide was passed over this catalyst in the reactordescribed in Example VII at a temperature of 353" C. and at a flow rateof 21 liters/hour. Infrared analysis of the oiigas showed the presenceof 5% by volume of ethyl fluoride, and the condensate in the Dry Icetrap contained ethyl fluoride, vinyl bromide, and methyl bromide. Theyield of ethyl fluoride was about 13% based on consumed ethane.

Example IX Three hundred and flfty cc. (436 g.) of cupric fluoridedihydrate was placed in the reactor described in Example VIII and heatedat C. in a stream of hydrogen fluoride until free from water. A mixtureof 31.5% ethane, 37% hydrogen fluoride, 21% oxygen, and 10.5% hydrogenbromide was then passed over this catalyst at a temperature of 348 C.and flow rate of 19 liters! hour. Infrared analysis showed the oflgas tocontain about 5% of ethyl fluoride.

when this example was repeated exactly, except that the temperature wasincreased to 471 C., infrared analysis disclosed the presence of 1-5%vinyl fluoride in the oiIgas together with some methyl fluoride,methylene fluoride, and fluorotorm.

Example X Example VIII was repeated, except that 350 cc. of cupricfluoride dihydrate was used as catalyst and the temperature was 500 C.The oflgas obtained in this manner was found by infrared analysis tocontain 540% of vinyl fluoride, and the Dry Ice trap contained someethyl fluoride. The yield of vinyl fluoride in this experiment was about15% calculated on ethane consumed.

Example XI Example VIII was repeated with a catalyst prepared by soaking350 cc. (61'? g.) of alpha-alumina in a solution of 200 g. of chromicnitrate in 250 cc. of water. The reaction temperature was 457 C. and theflow rate 21 liters/hour. In- Hand analysis showed the oflgas to containsome ethyl fluoride.

The process of this invention is applied most advantageously to thegaseous paraflln hydrocarbons, particularly those containing irom 1 to 5carbon atoms, both because of ease of operation and because they yieldfewer by-products. Examples of such hydrocarbons, in addition to thosealready mentioned, are propane, butane. isobutane and pentane. Examplesof higher hydrocarbons, namely. those containin up to 20 carbon atoms,that may be used are hexane. decane, cetane and eioosane. Mixtures ofhydrocarbons may also be used.

The molar or volume ratio of oxygen to paraf- Iln hydrocarbon can bevaried widely but is preferably kept within the range 1:3 to 3:1. Themolar ratio of oxygen to hydrogen fluoride can likewise be variedconsiderably. In general, however, this ratio should be kept between 1:5and 2:1.

In Examples I-III, V, and VI-XI, hydrogen bromide was included in thereaction mixture as a "promoter. The mechanism by which this agentfunctions is not known, but its use greatly increases the yield offluorohydrocarbon. Hydrogen chloride and iodide can also be used aspromoters. When hydrogen bromide, chloride, or iodide is used aspromoter, some bromo-, chloro-, or lode-substituted hydrocarbons areobtained. The molar ratio of oxygen: promoter should preferably exceed1:1 and is advantageously in the range 2:1 to 1.

Catalysts useful to this process are oxides and inorganic salts ofvariable valent metals, such as copper, lead, chromium. and the metalsranging in atomic number from 26 to 28 and constituting the group iron,cobalt and nickel. These catalysts are preferably made by treating asuitable support, such as alumina, calcium fluoride. or copper gauze,with an aqueous solution of an inorganic acid salt of the multivalentmetal, for example, the nitrate, sulfate, chloride, or other halide, andthen heating to remove the water. At reaction temperatures the salt maybe converted to the oxide or fluoride. The preferred catalysts areprepared from copper salts, such as cupric nitrate, cupric sulfate andcuprous chloride. Metal chromites, particularly copper chromite, arealso effective catalysts.

Owing to the high temperatures used in the fluorination process of thisinvention (325 to 700 and preferably 450-575 C.), the reaction mixt=xreis kept in the reaction zone for only a short time. Contact periodsranging from 5 to 60 seconds are normally used. Even under theseconditions little monofluoromethane is found in the product, presumablybecause of its thermal instability. The principal fluorinated productsobtained from methane are difluoromethane and trifluoromethane. Whenhydrocarbons higher than methane are used, some decomposition o'ccursparticularly at the higher temperatures, for fluoromethanes are presentin the products.

As indicated in the examples, the temperature and the catalyst have amarked effect on the course of the reaction. For example, when cupricfluoride is used as a catalyst in the fluori nation of ethane withhydrogen fluoride and hydrogen bromide at 325 to 575 C., ethyl fluorideis obtained in the lower temperature range and vinyl fluoride in thehigher tempera-t range. With this catalyst the most suitable te 4perature for the preparation of vinyl fiuorideris 450 to 550 C. Wheniron oxide is used in place of cupric fluoride, vinyl fluoride isobtained at both the lower and higher temperatures. the most suitabletemperatures being from 400 to 550 C. On the other hand, the use of leadoxide as catalyst favors the formation of ethyl fluoride over the entirerange (325 to 575 0.). In order to convert ethane to fluorinatedhydrocarbons containing two carbon atoms temperatures above 575 C.should be avoided.

The reaction must, of course, be carried out in 6 equipment that isresistant to hydrogen fluoride. As indicated in the examples, lnconelmetal is suitable for this. purpose. Monel metal, stainless steel, andnickel can also be used.

The fluorohydrocarbons obtained are useful in the same applications forwhich fluorohydrocarbons made by other methods are used, e. g.,refrigerants, heat transfer agents, and inter mediates for. thepreparation of other products. Thus. vinyl fluoride is useful in thepreparation of vinyl fluoride polymers and copolymers.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof. it is to beunderstood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims.

I claim:

1. A process for preparing fluorinated hydrocarbons which comprisesheating, in contact with a catalyst to reaction temperature within therange of 325 to 700 C., a mixture of a paraifln hydrocarbon, hydrogenfluoride, and oxygen, said catalyst being selected from the groupconsisting of inorganic salts and oxides of a variable valent metal.

2. The process set forth in claim 1 in which said paraffin hydrocarboncontains from 1 to 5 carbon atoms.

3. The process set forth in claim 1 in which said paraflin hydrocarbonis ethane.

4. A process for preparing fluorinated hydrocarbons which comprisesheating, in contact with a catalyst and a promoter to reactiontemperature within the range of 325 C. to 700 C., a gaseous mixture of aparaflln hydrocarbon having from 1 to 5 carbon atoms, hydrogen fluoride.and oxygen, said catalyst being selected from the group consisting ofinorganic salts and oxides of a variable valent metal, said promoterbeing a hydrogen halide which is a member of the group consisting ofhydrogen chloride, hydrogen bromide and hydrogen iodide.

5. The process set forth in claim 4 in which said promoter is hydrogenbromide.

6. The process set forth in claim 4 in which the oxygen is contained insaid mixture in an oxygen to paraflin mole ratio of from 1:3 to 3:1

and in an oxygen to hydrogen fluoride ratio of from 1:5 to 2:1.

7. The process set forth in claim 4 in which said paraifln hydrocarbonis ethane.

8. A process for preparing fluorinated hydrocarbons which comprlsesheating, in contact with a catalyst and hydrogen bromide as a promoterto reaction temperature within the range of 458 C. to 575 C., a gaseousmixture of ethane, hydrogen fluoride, and oxygen, wherein said oxygen ispresent in an oxygen to ethane mole ratio of from 1:3 to 3:1 and in anoxygen to hydrogen fluoride ratio of from 1:5 to 2:1, said catalystbeing selected from the group consisting of inorganic salts and oxidesof a variable valent metal.

GERALD M. WHITMAN.

REFERENCES CITED UNITED STATES PATENTS Name Date Krause et al. Jan. 3,1928 Number Certificate of Correction December 18, 1951 Patent No.2,578,913

GERALD M. WHITMAN It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correctionas follows:

Column 4, line 33, for Example VIII read Example VII column 6, line 56,for 458 read 450 and that the said Letters Patent should the same mayconform to the record of the case in the Patent Oifice.

Signed and sealed this 18th day of March, A. D. 1952.

be read as corrected above, so that THOMAS F. MURPHY,

Assistant Commissioner of Patents.

1. A PROCESS FOR PREPARING FLUORINATED HYDROCARBONS WHICH COMPRISESHEATING, IN CONTACE WITH A CATALYST TO REACTION TEMPERATURE WITHIN THERANGE OF 325* TO 700* C., A MIXTURE OF A PARAFFIN HYDROCARBON, HYDROGENFLUORIDE, AND OXYGEN, SAID CATALYST BEING SELECTED FROM THE GROUPCONSISTING OF INORGANIC SALTS AND OXIDES OF A VARIABLE VALENT METAL.